1. Field of the Invention
The present invention relates to a thermal transfer recording medium of thermal fusion type, capable of stably forming high-quality transferred images over a long period of time.
2. Description of the Related Art
In a thermal fusion type transfer recording method, a thermal transfer ink sheet (thermal transfer recording medium) is heated using thermal energy of a laser, a thermal head, etc. controlled with an electrical signal, and the fused ink is transferred onto a transfer target object to record an image.
Ink layers that are each composed mainly of wax as a thermally fusible material, as well as a colorant, are becoming popular as ink layers of thermal transfer recording media of this sort. For example, carnauba wax is favorably used.
The carnauba wax is advantageous in that it yields superior rub resistance (because it is a hard wax), superior sensitivity characteristics (because of its low melting point) and superior printing characteristics (because of its sharp heat-related changeability and low melt viscosity). For example, the carnauba wax is used for the purpose of forming transferred images superior in rub resistance and lubricity (refer to Japanese Patent Application Laid-Open (JP-A) Nos. 06-293188 and 09-156240).
Also, the carnauba wax has conventionally been made aqueous and used in the form of emulsion. In such cases, when the emulsion is heated with a thermal head, cutting and resultant separation preferentially take place at boundaries between particles forming the emulsion. The cut and separated pieces are transferred to the surface of a transfer target object. Therefore, edges of transferred matter (printed matter) are very sharp, and, due to the aqueousness of the emulsion, its environmental load can be reduced.
Here, when the aqueous emulsion of the carnauba wax is formed, an emulsifier is generally used. For example, an organic fatty acid is used as this emulsifier (refer to Japanese Patent (JP-B) No. 3835956). In a case where only an organic fatty acid is used as the emulsifier, the carnauba wax can be emulsified with ease. However, the following problem exists: despite the fact that the carnauba wax is first completely melted at the time of the formation of the aqueous emulsion, blooming of the carnauba wax occurs as time passes, even after cooling, because of its supercooled nature. Therefore, when the thermal transfer recording medium is stored in the form of a roll, the surface of a back layer (which is provided over a support included in the thermal transfer recording medium) is smeared, and thus stable formation of high-quality transferred images over a long period of time impossible.